15-3sum.md Added Python solution.

gazeldx · gazeldx · commit 61293fcc366a · 2025-01-05T17:44:04.000+08:00
diff --git a/README.md b/README.md
@@ -14,7 +14,7 @@ You can skip the more difficult problems and do them later.
 
 # Array
 - [704. Binary Search](solutions/1-1000/704-binary-search.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
-- [27. Remove Element](solutions/1-1000/27-remove-element.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **2** solutions.
+- [27. Remove Element](solutions/1-1000/27-remove-element.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **2** ways.
 - [977. Squares of a Sorted Array](solutions/1-1000/977-squares-of-a-sorted-array.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
 - [209. Minimum Size Subarray Sum](solutions/1-1000/209-minimum-size-subarray-sum.md) was solved in _Python, Java, JavaScript, C#_.
 - [303. Range Sum Query - Immutable](solutions/1-1000/303-range-sum-query-immutable.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
@@ -35,6 +35,7 @@ You can skip the more difficult problems and do them later.
 - [1. Two Sum](solutions/1-1000/1-two-sum.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
 - [202. Happy Number](solutions/1-1000/202-happy-number.md) was solved in _Python, Java, JavaScript, C#_.
 - [454. 4Sum II](solutions/1-1000/454-4sum-ii.md) was solved in _Python, Java, JavaScript, C#, Ruby_.
+- [15. 3Sum](solutions/1-1000/15-3sum.md) was solved in _Python_ and 2 ways.
 
 # Dynamic Programming
 ## Basics
@@ -43,12 +44,12 @@ You can skip the more difficult problems and do them later.
 ## House Robber
 - [198. House Robber](solutions/1-1000/198-house-robber.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
 - [213. House Robber II](solutions/1-1000/213-house-robber-ii.md) was solved in _Python, JavaScript, Go_.
-- [337. House Robber III](solutions/1-1000/337-house-robber-iii.md) was solved in _Python, JavaScript, Go_ and **2** solutions.
+- [337. House Robber III](solutions/1-1000/337-house-robber-iii.md) was solved in _Python, JavaScript, Go_ and **2** ways.
 
 ## Knapsack Problems
 ### 0/1 Knapsack
-- [416. Partition Equal Subset Sum](solutions/1-1000/416-partition-equal-subset-sum.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **2** solutions.
-- [1049. Last Stone Weight II](solutions/1001-2000/1049-last-stone-weight-ii.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **2** solutions.
+- [416. Partition Equal Subset Sum](solutions/1-1000/416-partition-equal-subset-sum.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **2** ways.
+- [1049. Last Stone Weight II](solutions/1001-2000/1049-last-stone-weight-ii.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **2** ways.
 - [494. Target Sum](solutions/1-1000/494-target-sum.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
 - [474. Ones and Zeroes](solutions/1-1000/474-ones-and-zeroes.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
 
@@ -81,20 +82,20 @@ You can skip the more difficult problems and do them later.
 # Monotonic Stack
 - [739. Daily Temperatures](solutions/1-1000/739-daily-temperatures.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
 - [496. Next Greater Element I](solutions/1-1000/496-next-greater-element-i.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
-- [42. Trapping Rain Water](solutions/1-1000/42-trapping-rain-water.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **2** solutions.
+- [42. Trapping Rain Water](solutions/1-1000/42-trapping-rain-water.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **2** ways.
 - [84. Largest Rectangle in Histogram](solutions/1-1000/84-largest-rectangle-in-histogram.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
 
 # Graph Theory
-- [797. All Paths From Source to Target](solutions/1-1000/797-all-paths-from-source-to-target.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **2** solutions.
-- [200. Number of Islands](solutions/1-1000/200-number-of-islands.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **3** solutions.
-- [463. Island Perimeter](solutions/1-1000/463-island-perimeter.md) was solved in _Python_ and **2** solutions.
+- [797. All Paths From Source to Target](solutions/1-1000/797-all-paths-from-source-to-target.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **2** ways.
+- [200. Number of Islands](solutions/1-1000/200-number-of-islands.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and **3** ways.
+- [463. Island Perimeter](solutions/1-1000/463-island-perimeter.md) was solved in _Python_ and **2** ways.
 - [695. Max Area of Island](solutions/1-1000/695-max-area-of-island.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
 - [827. Making A Large Island](solutions/1-1000/827-making-a-large-island.md) was solved in _Python_.
 - [127. Word Ladder](solutions/1-1000/127-word-ladder.md) was solved in _Python_.
-- [1971. Find if Path Exists in Graph](solutions/1001-2000/1971-find-if-path-exists-in-graph.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and 2 solutions.
+- [1971. Find if Path Exists in Graph](solutions/1001-2000/1971-find-if-path-exists-in-graph.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and 2 ways.
 - [684. Redundant Connection](solutions/1-1000/684-redundant-connection.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_.
 - [685. Redundant Connection II](solutions/1-1000/685-redundant-connection-ii.md) was solved in _Python_.
-- [1584. Min Cost to Connect All Points](solutions/1001-2000/1584-min-cost-to-connect-all-points.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and 2 solutions.
-- [207. Course Schedule](solutions/1-1000/207-course-schedule.md) was solved in _Python, Java, C++, C#_ and 2 solutions.
+- [1584. Min Cost to Connect All Points](solutions/1001-2000/1584-min-cost-to-connect-all-points.md) was solved in _Python, Java, C++, JavaScript, C#, Go, Ruby_ and 2 ways.
+- [207. Course Schedule](solutions/1-1000/207-course-schedule.md) was solved in _Python, Java, C++, C#_ and 2 ways.
 
 More LeetCode problems will be added soon...
diff --git a/solutions/1-1000/1-two-sum.md b/solutions/1-1000/1-two-sum.md
@@ -31,7 +31,7 @@ Difficulty: **Easy**
 - `-10**9 <= target <= 10**9`
 - **Only one valid answer exists.**
 
-## Solution 1
+## Solution 1: Two pointers (should master)
 [中文题解](#中文题解)
 
 1. The time complexity of the brute force solution is `O(n**2)`. To improve efficiency, you can sort the array, and then use **two pointers**, one pointing to the head of the array and the other pointing to the tail of the array, and decide `left += 1` or `right -= 1` according to the comparison of `sum` and `target`.
@@ -41,7 +41,7 @@ Difficulty: **Easy**
 * Time: `O(N * log N)`.
 * Space: `O(N)`.
 
-## Solution 2
+## Solution 2: Use Map (also should master)
 1. In `Map`, `key` is `num`, and `value` is array `index`.
 2. Traverse the array, if `target - num` is in `Map`, return it. Otherwise, add `num` to `Map`.
 
@@ -73,6 +73,12 @@ for (let i = 0; i < nums.length; i++) {
 * Space: `O(n)`.
 
 ## Java
+### Solution 1: Two pointers
+```java
+// Welcome to create a PR to complete the code, thanks!
+```
+
+### Solution 2: Using Map
 ```java
 class Solution {
     public int[] twoSum(int[] nums, int target) {
@@ -92,19 +98,6 @@ class Solution {
 ```
 
 ## Python
-### Solution 2: Using Map
-```python
-class Solution:
-    def twoSum(self, nums: List[int], target: int) -> List[int]:
-        num_to_index = {}
-        
-        for i, num in enumerate(nums):
-            if target - num in num_to_index:
-                return [num_to_index[target - num], i]
-
-            num_to_index[num] = i
-```
-
 ### Solution 1: Two pointers
 ```python
 class Solution:
@@ -130,7 +123,26 @@ class Solution:
         return [original_nums.index(nums[left]), len(nums) - 1 - original_nums[::-1].index(nums[right])]
 ```
 
+### Solution 2: Using Map
+```python
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        num_to_index = {}
+        
+        for i, num in enumerate(nums):
+            if target - num in num_to_index:
+                return [num_to_index[target - num], i]
+
+            num_to_index[num] = i
+```
+
 ## C++
+### Solution 1: Two pointers
+```cpp
+// Welcome to create a PR to complete the code, thanks!
+```
+
+### Solution 2: Using Map
 ```cpp
 class Solution {
 public:
@@ -151,6 +163,12 @@ public:
 ```
 
 ## JavaScript
+### Solution 1: Two pointers
+```javascript
+// Welcome to create a PR to complete the code, thanks!
+```
+
+### Solution 2: Using Map
 ```javascript
 var twoSum = function (nums, target) {
   let numToIndex = new Map()
@@ -166,6 +184,12 @@ var twoSum = function (nums, target) {
 ```
 
 ## C#
+### Solution 1: Two pointers
+```c#
+// Welcome to create a PR to complete the code, thanks!
+```
+
+### Solution 2: Using Map
 ```c#
 public class Solution {
     public int[] TwoSum(int[] nums, int target) {
@@ -185,6 +209,12 @@ public class Solution {
 ```
 
 ## Go
+### Solution 1: Two pointers
+```go
+// Welcome to create a PR to complete the code, thanks!
+```
+
+### Solution 2: Using Map
 ```go
 func twoSum(nums []int, target int) []int {
     numToIndex := map[int]int{}
@@ -202,6 +232,12 @@ func twoSum(nums []int, target int) []int {
 ```
 
 ## Ruby
+### Solution 1: Two pointers
+```ruby
+# Welcome to create a PR to complete the code, thanks!
+```
+
+### Solution 2: Using Map
 ```ruby
 def two_sum(nums, target)
   num_to_index = {}
diff --git a/solutions/1-1000/15-3sum.md b/solutions/1-1000/15-3sum.md
